Page 328 - HVAC Pump Handbook

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Source: HVAC Pump Handbook

Chapter
11

Open Cooling Tower Pumps

11.1 Introduction
Most of the air-conditioning systems in the HVAC industry or process
cooling systems having a net cooling capacity in excess of approxi-
mately 4,000,000 Btu/h (333 tons) transmit the heat load to the
atmosphere evaporatively through an open cooling tower. Evaporating
a pound of water removes around 1000 Btu from the remaining water.
This equates to about 1 percent of the water flow being evaporated to
cool the balance of the water over a temperature difference of 10°F at
design conditions. This is in contrast to the “once-through” water cool-
ing systems (100 percent makeup), in which only 10 Btu are removed
when 1 lb of water is cooled 10°F.
Cooling towers were developed to take the place of lakes and spray
ponds, which required considerable space to accomplish the same
amount of evaporative heat transfer. The cooling tower industry pros-
pered as system owners and operators were told that water was a
valuable commodity that should not be wasted. Once-through water
cooling systems have been outlawed in many parts of the world.
Since the evaporative process depends on wet-bulb temperature, a
water-cooled refrigerant condenser is significantly more efficient than
an air-cooled condenser. The air-cooled condenser must be designed
for the highest dry-bulb temperature that will be encountered on each
specific application.
Cooling towers have been the subject of much research to achieve
the most efficient operation and the maximum amount of capacity
per cubic foot of tower volume. Cooling towers are normally rated in
tons of cooling, 12,000 Btu/ton. Alternate ratings are in gallons per

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